Scientists have come one step closer to finding a cure for baldness after identifying a potential cause of the condition.

The ability to reverse thinning hair could soon become a reality thanks to researchers in the US who have discovered a protein that triggers hair loss.

This discovery could lead to a cream to treat baldness.

The majority of men begin to bald in middle age, and approximately 80% of men experience some hair loss by the age of 70.

Genetics and testosterone (the male sex hormone) play a major part role in balding, causing the hair follicles to shrink. These follicles eventually become so small that they are invisible, resulting in the appearance of baldness.

University of Pennsylvania researchers studied bald men and lab mice to determine which genes are switched on when men start to go bald.

They found that levels of a protein called prostaglandin D synthase are higher in the cells of hair follicles present in bald patches on the scalp, but not in the areas were normal hair grew.

Transplanted human hairs stopped growing when given the protein.

Professor George Cotsarelis,who led the research, said: "Essentially we showed that prostaglandin protein was elevated in the bald scalp of men and that it inhibited hair growth. So we identified a target for treating male-pattern baldness.

"The next step would be to screen for compounds that affect this receptor and to also find out whether blocking that receptor would reverse balding or just prevent balding - a question that would take a while to figure out."

Several known drugs that target baldness have already been identified, he said, and some are even in clinical trials.

Researchers now say there is scope for developing a treatment that can be applied to the scalp to prevent baldness and to potentially help thinning hair to regrow.